Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $22.91   13.360%   $25.9708   $25.97   $25.95   $26.00  
  Purchase #2 $66.66   5.752%   $70.4943   $70.49   $70.50   $70.50  
  Purchase #3 $145.45   5.695%   $153.7334   $153.73   $153.75   $153.70  
  Purchase #4 $92.90   4.332%   $96.9244   $96.92   $96.90   $96.90  
  Purchase #5 $51.39   10.655%   $56.8656   $56.87   $56.85   $56.90  
  Purchase #6 $226.34   9.286%   $247.3579   $247.36   $247.35   $247.40  
  Purchase #7 $214.94   7.691%   $231.471   $231.47   $231.45   $231.50  
  7 purchase totals = $820.59       $882.8174   $882.81   $882.75   $882.90